[ RadSafe ] FW: Reporter's question about lower limitsofdetection

[Brennan, Mike (DOH)]

The number of km driven does not give you good information about how
much air was pulled through the filter, for the simple reason that
distance traveled in an uncontrolled environment does not correlate to
the amount of air that was pulled through the engine.  I have, over the
years, made a number of trips from my home to the nearest major airport,
about 45 miles away.  I have made the trip in as little as 45 minutes,
when traveling in the early morning when traffic was light.  I have also
made the trip in almost 2 hour during the middle of the day.  Same
distance, very different times, gas mileage, and amount of air through
the filter.  Additionally, the daytime trip probably had more
particulate in the air to act as sites for contamination (including
radioactive material) to attach to.  

Given that you could have used a vacuum cleaner with a filter over the
hose, and calibrated the flow with little trouble, I have to admit to
the suspicion that you chose the automobile filter specifically BECAUSE
of the unknowns, which you could manipulate to support your agenda.  



-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Busby, Chris
Sent: Sunday, August 07, 2011 5:39 AM
To: parthasarathy k s; The International Radiation Protection (Health
Physics) Mailing List; SAFarber at optonline.net; The International
Radiation Protection (Health Physics) Mailing List; The International
Radiation Protection (Health Physics) Mailing List
Subject: Re: [ RadSafe ] FW: Reporter's question about lower
limitsofdetection



Dear Radsafers,
It was my intention to show that the levels in Japan in air were not
trivial. I do know this because I have measured it in several car
filters for which the engine size is known and the number of km driven
after the incident is known. The efficiency of the filters is assumed to
be 50% but this is not known for sure although I have asked the
manufacturers. The filters showed between 1.2 and 3Bq per cu metre of
Cs-137. This can be compared with the attached data from Harwell. The
results were from my lab and also from Harwell who we paid to do the
analysis. 
I am interested to learn that the levels were higher in the USA during
the atmospheric tests than in the UK: Stewart Farber says 100mBq/m3.
Probably because the US is where many of the tests were done.
But my argument was about Japan, not levels in the USA. I am quite aware
that the levels in the USA were far smaller, as we would expect. But i
see a maximum of 0.116pCi is 4.29mBq/m3 The average is 0.7mBq/m3.
Compare with the graph attached. But I think it depends on where you
live, doesnt it? And what other stuff comes along as a passenger.


Cheers
Chris

Oranges:

The US EPA made excellent measurements of airborne Cs-137 in the US
released from Fukushima after the accident. Air particulate samples were
taken all over the USA by the EPA. Based on calibrated Hi-Vo samplers
and calibrated counting geometry for air filters, the highest levels of
Cs-137 in air measured were seen in HI, CA, AZ, NV. Cs-137 levels were
reported as [picoCuries per cubic meter]:

Minimum: 0.000238 pCi/m^3
Maximum: 0.116
Average: 0.0189

The above EPA data can be seen at:
<http://oaspub.epa.gov/enviro/erams_query_v2.simple_output?Llocation=EPA
+Reg
ion&subloc=09&media=AIR-FILTER&radi=Cesium-137&Fromyear=2011&Toyear=2011
&uni
ts=Traditional>


Open air testing of 500 nuclear bombs by the US and Soviets, ending in
1963, led to many years of significant ongoing nuclear fallout from the
mid 1950s, reaching a peak level of total terrestrial deposition in
1968. After 1968 the environmental inventory of Cs-137 and Sr-90
continued to drop steadily with minor blips in the US from small nuclear
bomb tests by India and China.
Chernobyl added no more than 1% to the environmental fallout inventory
in the US.

During the MANY YEARS of nuclear test fallout airborne Cs-137 in
essentially the entire Northern Hemisphere, including the US, was
roughly about 0.1 pCi/m^3. Peak levels of airborne Cs-137 during the
period of open air testing were commonly measured at 0.5 pCi/m^3 and
higher.

As noted above, the EPA measured a SHORT TERM average of airborne Cs-137
in the US from Fukushima of 0.0189 pCi/m^3  in those states having the
highest measured concentrations.

The LONG-TERM average level of airborne Cs-137 in the US during the many
years of atomic bomb fallout during and for a few years after open air
testing ended was about 5 times higher than the average SHORT TERM peak
levels of accurately sampled and measured airborne Cs-137 seen in the US
from Fukushima [based upon a few measurements fading away to essentially
nothing after a short time].

Given that what is important in calculating total radiation dose is the
ratio of the time integrated concentration of airborne exposure to
Cs-137 in this case,  the total exposure of people in the US from open
air testing fallout is at least 500 times greater than the total
exposure from short-term peak airborne Cs-137 in the US measured after
the Fukushima accident [in looking at the areas in the US that had the
highest recent airborne Cs-137 levels].

And yes, I consider total time-integrated exposure to Fukushima airborne
Cs-137 and Sr-90 in the US that is about one part in 500  [or less] of
the time integrated radiation exposure from nuclear bomb test fallout in
the US to be trivial. -Oranges